I searched for this topic/issue and came up empty, so my appologizes if this has been discussed in the past. I recently installed a 12.5" Weaponkraft full floating handguard on to my 16" Bushy XM15. I tightened their proprietary barrel nut to 35 ft. lbs. as instructed. The issue is now it is very difficult to jack a live round out of the chamber after it has gone into battery. The live rounds chamber and lock normally. I completely disassembled the bolt carrier and head, and closely inspected the barrel extension for debris or anything else that might cause this. It is as if after installing the forearm, the head space has been minimized. I know that the the headspacing is set off of the barrel extension, therefore in theory, playing with the barrel nut won't/can't affect it. Any ideas or suggestions will be greatly appreciated. Thanks in advance.

Compare the center of the barrel feed ramps to the center of the front take down lug.

Could be that when you were tightening the barrel nut (read should have been 35fl of torque, then no more than 80ftlbs to get the barrel nut gas tube passage to align with the upper receiver gas tube channel), the barrel could have slipped, with the barrel extension lugs no longer correctly aligned to the bolt lugs.

Also on the subject of the gas tube channel, with the carrier alone (bolt pulled off) dry fit it only the carrier into the upper receiver to confirm that the gas tube is correctly indexed with the carrier key, and that the gas tube is free moving in the upper receiver/barrel nut channels for it (see part one about making sure that the upper receiver and barrel nut channel as in line.

I will check the feed ramp alignment. What I have found is without a cartridge, the carrier and bolt lock up smoothly, the gas tube seems to be aligned perfectly with the carrier gas key. There didn't seem to be any play at the barrel alignment pin. I am wondering now if perhaps the barrel extension didn't rotate a tiny bit in relation to the barrel itself, thereby actually changing the head space. The barrel nut that comes with this forearm uses a weird two piece set. It has a large collar with a hole for the gas tube, the collar threads onto the receiver but it is not tightened against the receiver. The clolar remains loose and the gas holes are kept in alignment using a drill bit. Then a threaded bushing is screwed into the collar until it bottoms out onto the barrel extension. This bushing is the portion of two piece nut assembly that is torqued. Live rounds chamber normally when the rifle is charged manualy or if the bolt release is hit. I haven't fired it yet, perhaps after a few rounds it will "loosen up" ?

You are using the same barrel as before, just changed the handguard, correct?

Headspace would not cause the symptoms you are experiencing.

Barrel extensions should be torqued to 150 ft/lbs, it's exceptionally unlikely that you tightened one.

I would agree with Dano, probably the most likely explanation is that the barrel/barrel extension are no longer in the proper orientation in the receiver, such that the bolt is not completely unlocking and the bolt lugs are snagging on the edges of the barrel extension lugs.

You have to remember that the "pin" is on the barrel extension, and the barrel extension is threaded on the barrel. To spec the barrel extension is torqued to 150 ft/lb's on the barrel, so if the extension was put on properly, you should not be able to turn the barrel extension while torquing the barrel assembly to the upper receiver (35ft/b's- 80 ft/lb's).

I will add some pictures once I get home tonight. I guess I am surprised that lock up would be so hyper sensitive to the rotational index of the barrel (extension). Even if the slot in the upper receiver were "wallered" out, it would only allow a few thousands of an inch of tortional deflection. Unless what you are saying is that the bolt head is actually over caming into the extension lugs, do to this slight indexing variation, and engaging in rough spots that previously were unmolested by the bolt going into battery? I wish I had some Prusian blue.

What the hell happened to the face of the barrel extension????
Looks like someone was pounding at it with a 6lb sledge hammer.

Next is the signs of low bullet feeds striking the front of the upper receiver below the ramps.

And yes, the barrel extension looks rotated in the upper receiver, but looks like the extension pin was bent pulling the barrel off, and not slipped the other was as the barrel nut was being re-tightened.

What looks like "pound" marks, I can assure you is only discoloration, no tools were used to remove the barrel except for wrench to loosen barrel nut. The mark under the feed ramp is a scratch made by a pocket screw driver I used to pursuade the bolt out of battery the first time it got stuck. The picture looks worse than it is. As far as it looking indexed improperly to you, what reference point are you using as a comparator? It looks as if it is aligned perfectly to me. Of course that is the problem...Obviously I am not seeing what is going on.

But I use the center of the gas tube channel, and the center of the front take down lug.

As for the real test, pull the upper receiver off the lower, then with it upside down, insert the B/C in and see if the center of the bolt lugs are indexing center wise with the receiver extension lugs.

Next to weed out a chamber problem alone (such as not getting it correctly clean, or a problem with reloaded ammo), without the B/C, muzzle straight down, drop a round into the chamber, use a wood dowel, tap the back of the case to make sure that the shoulders of the round are fully mated against the shoulder in the chamber, then turn the muzzle straight up. The live round should fall right out.

If a factory loaded live round does not fall out of the chamber (and you have been using a chamber brush to clean the chamber with CLP, then using a sharpie pen, and smoke the bullet of the round. Now do the test again, and this time after you use a cleaning rod to tap out the live round from the chamber, look at the bullet for any signs(scrap marks on the smoked section of the bullet) of embedding into the rifling at loading.

If the problem is with reloaded ammo, then first use an ammo test gauge. This will tell you if the cases where not correctly trimmed, if you are long loading too long, or even if you over crimped the bullet, ending up with the shoulders of the case slightly bulged.

That you have set the sizer to kiss the shell holder under actual ram tension of sizing a case. If you set the sizer up without this increased tension, then bank when you went to a sizer a case, there was a huge gap between the sizer and holder, meaning that the case was not fully sized.

You have to trim the cases, or they are going to be too long after even a single to few firings. I have listed this after sizing, since the case needed to be sized first, then trimmed.

When seating a bullet, a little crimp pressure goes a long way!!!!! If you try to use as much crimping pressure as say a hand gun round, your going to budge the shoulder of the case every time. Here, a round test gauge comes in handy to check some of the loaded rounds from time to time. And unless you are using a Lee FLD crimper, then trimming the all the case to uniform is required.

Lastly, if you are loading to come out of the mag, should not be a problem, but when you start to long load to sled rounds, make sure that you are not hanging the bullet so far out of the case that you start rifle embedding on the charge.

I opened a brand new box of Federal 5.56 and spent 10 min. painting a few rounds with a blue sharpie. Place it in the chamber and hit the bolt release. Pulled back the charging handle and exgracted the round with zero effort, and there were no marks on the case. I did this several more times with different factory rounds. Then I tried a "new" batch of reloads, same thing, no problems or hangups whatsoever. Apparantly, it's jusg my luck that the first few reloads I tried to cycle were "out of spec.". To add insult to injury, I can't locate the exact rounds that were giving me trouble initially! I just threw them back into the pile that was on my bench.. I will have to allocate those 60 rounds to target practice only. Upshot is, I greatly appreciate your help, and next time I will exercise due diligence prior to wasting everyone's time on this forum.